This invention relates to a medical instrument which is designed to be inserted into a patient's body through the instrument guiding channel of an endoscope, already inserted into the patient's body, for continuously cutting living tissue and collecting a plurality of living tissue samples.
International Publication PCT WO95/08291, for example, discloses a medical instrument for sampling living tissue. FIG. 13A shows an essential part of a medical instrument (a) described in the publication. The medical instrument (a) has a flexible sheath (b) which can be inserted into an endoscope. The sheath (b) has an opening (d) at its distal end. A small-diameter inner tube (c) is inserted in the sheath (b). The inner tube (c) is fixed on the inner peripheral surface of the sheath (b).
An operational wire (e) is inserted in the inner tube (c). A looped cutting wire (h) is connected to an end of the operational wire (e). The cutting wire (h) can be protruded to the outside of the opening (d) of the flexible sheath (b) by operating the operational wire (e).
When the operational wire (e) has been pulled to the hand side, the cutting wire (h) is retreated into the flexible sheath (b) and the loop of the wire (h) is contracted.
When the operational wire (e) has been pushed, the cutting wire (h) is protruded to the outside of the sheath (b) through the opening (d). At this time, the loop of the cutting wire (h) expands due to its elastic force such that it crosses the opening (d). A retractor (f) is provided in the flexible sheath (b) for pushing and moving an excised tissue piece (p).
When using the medical instrument (a), it is inserted into the forceps channel of the endoscope. Then, the operational wire (e) is pushed to protrude the cutting wire (h) to the outside of the sheath (b) and expand it. In this state, living tissue is inserted into the sheath (b) through the opening (d) using the cutting wire (h).
After that, the operational wire (e) is pulled to the hand side, thereby pulling the cutting wire (h) into the flexible sheath (b). At this time, the loop diameter of the cutting wire (h) is gradually reduced while it is pulled into the flexible sheath (b). The living tissue already inserted in the sheath (b) is cut by the tightening force of the gradually diameter-reduced wire (h). The excised tissue piece (p) is contained in a tissue storing space (g) defined in the sheath (b).
This cutting operation is repeated a necessary number of times, and a plurality of excised tissue pieces p1, p2, p3 and p4 are sequentially stored in the tissue storing space (g). Thereafter, the medical instrument (a) is removed from the endoscope, and the retractor (f) is protruded to the outside of the sheath through the opening (d), thereby pushing the excised tissue pieces p1, p2, p3 and p4 out of the tissue storing space (g). Thus, the tissue pieces are collected.
European Patent EP 0761170 discloses a medical instrument of another structure. As is shown in FIG. 13B, it discloses a medical instrument (k) which has an outer cylinder (i), and a looped cutting wire (j) which can expand at an end of the outer cylinder (i). In this case, a living tissue piece is excised by pulling the cutting wire (j) from the end of the outer cylinder (j) into it.
Moreover, Japanese Patent Application No. 8-310664 (this document was published on Jun. 12, 1998 (KOKAI publication No. 10-146345) and had not yet been published when the present application was filed) discloses a medical instrument for endoscopes, which excises living tissue through an endoscope when a high frequency current is flown. In this case, as shown in FIG. 13C, an operational wire (q) is axially movably provided in a flexible sheath (m). A substantially looped cutting wire (n) is mounted at an end of the operational wire (q) such that it can protrude out of and retreat into the sheath (m). When a high frequency current is flown into the cutting wire (n) via the operational wire (q), it can excise living tissue.
Further, in this instrument, the sheath (m) has a slotted end portion (o). The loop of the cutting wire (n) is engaged with the slotted portion (o) when the wire (n) is pulled into the sheath (m). Where the loop of the cutting wire (n) is engaged with the slotted portion (o) of the sheath (m), the direction of the high frequency cutting wire (n) can be changed by rotating the wire (n) together with the sheath (m) when axially rotating the sheath (m).
When, in the case of the medical instrument disclosed in PCT WO95/08291, the cutting wire (h) has been pulled out of the flexible sheath (b) and has expanded due to its own elastic force, the expanded section of the wire (h) must be situated at the opening (d) of the sheath in order to excise tissue in good condition by the wire (h).
Since, however, the cutting wire (h) inserted in the sheath (b) is a relatively slender flexible wire, it may not sufficiently follow the rotation of the sheath (b). Accordingly, where the sheath (b) can easily rotate about its axis as in the operation of inserting the medical instrument (a) into the endoscope, it is highly possible that the cutting wire (h) inserted in the sheath (b) will not follow the axial rotation of the sheath (b). In this case, it is possible that the expanded section (h) of the cutting wire (h) will be displaced from the opening (d) of the flexible sheath (b) when the medical instrument (a) protrudes from the tip of the endoscope, thereby disabling collection of tissue.
Moreover, to correct the displacement of the expanded section of the cutting wire (h) from the opening (d) of the sheath (b), it is necessary to rotate the expanded section relative to the opening (d). Thus, handling of the medical instrument (a) is too much trouble.
Furthermore, European Patent EP 0761170 discloses means for limiting the direction of expansion of the cutting wire (j) by providing strap (s) at an end of the wire (j) and fixing one end of strap (s) to the outer peripheral surface of the outer cylinder (i).
In this case, however, fixing the strap (s) on the outer peripheral surface of the outer cylinder (i) inevitably complicates the structure of the medical instrument (k) and increases the outer diameter of the entire insertion section of the instrument (k). Accordingly, it is difficult to reduce the outer diameter of the entire insertion section to an extent which enables insertion of the insertion section of the instrument (k) into the forceps channel of the endoscope.
In addition, the strap (s) of the cutting wire (j) limit the movement of the wire (j) toward the axis of the outer cylinder (i). Thus, the strap (s) not only reduce the degree of freedom of the movement of the wire (j), but also become obstacles when grasping tissue by the wire (j).
In the case of the structure described in Japanese Patent Application No. 8-310664, a rather sharp edge portion may be formed at the slotted portion (o) of the sheath (m) with which the cutting wire (n) is engaged. This sharp edge portion may damage the wall surface of the forceps channel of the endoscope while the medical instrument is inserted into it, or may injure a mucous membrane in a cavity of the body.